507 research outputs found
Dense molecular clouds in the SN2008fp host galaxy
(abridged) We use observations of interstellar absorption features, such as
atomic and molecular lines as well as diffuse interstellar bands (DIBs),
towards SN2008fp to study the physical properties of extra-galactic diffuse
interstellar clouds in the host galaxy, ESO428-G14. The properties of the
intervening dust are investigated via spectropolarimetry. The spectra of
SN2008fp reveal a complex of diffuse atomic clouds at radial velocities in line
with the systematic velocities of the host galaxy (~1700 km/s). A translucent
(A_V ~ 1.5 mag) cloud is detected at a heliocentric velocity of 1770 km/s This
cold dense cloud is rich in dense atomic gas tracers, molecules, as well as
diffuse interstellar bands. We have detected both C2 and C3 for the first time
in a galaxy beyond the Local Group. The CN (0,0) band line ratios are used to
derive an in-situ measurement of the cosmic background radiation temperature in
an external galaxy; this gives an excitation temperature of T = 2.9 +- 0.3 K.
The interstellar polarization law deviates significantly from what is observed
in the Galaxy, indicating substantial differences in the composition or size
distribution of dust grains in the SN2008fp host galaxy. C2 is used to probe
the cold diffuse ISM density and temperature. The lack of variability in the
extra-galactic absorption line profiles over a period of one month implies that
the absorbing material is not circumstellar and thus not affected directly by
the SN event. Also it shows that there are no significant density variation in
the small-scale structure of the molecular cloud down to 100 AU.Comment: 10 pages. Accepted for publication in A&A. Revisions include several
small correction
Studying the small scale ISM structure with supernovae
AIMS. In this work we explore the possibility of using the fast expansion of
a Type Ia supernova photosphere to detect extra-galactic ISM column density
variations on spatial scales of ~100 AU on time scales of a few months.
METHODS. We constructed a simple model which describes the expansion of the
photodisk and the effects of a patchy interstellar cloud on the observed
equivalent width of Na I D lines. Using this model we derived the behavior of
the equivalent width as a function of time, spatial scale and amplitude of the
column density fluctuations.
RESULTS. The calculations show that isolated, small (<100 AU) clouds with Na
I column densities exceeding a few 10^11 cm^-2 would be easily detected. In
contrast, the effects of a more realistic, patchy ISM become measurable in a
fraction of cases, and for peak-to-peak variations larger than ~10^12 cm^-2 on
a scale of 1000 AU.
CONCLUSIONS. The proposed technique provides a unique way to probe the
extra-galactic small scale structure, which is out of reach for any of the
methods used so far. The same tool can also be applied to study the sub-AU
Galactic ISM structure.Comment: 6 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
High Redshift Supernovae in the Hubble Deep Field
Two supernovae detected in the Hubble Deep Field using the original December
1995 epoch and data from a shorter (63000 s in F814W) December 1997 visit with
HST are discussed. The supernovae (SNe) are both associated with distinct
galaxies at redshifts of 0.95 (spectroscopic) from Cohen etal. (1996) and 1.32
(photometric) from the work of Fernandez-Soto, Lanzetta, and Yahil (1998).
These redshifts are near, in the case of 0.95, and well beyond for 1.32 the
greatest distance reported previously for SNe. We show that our observations
are sensitive to SNe to z < 1.8 in either epoch for an event near peak
brightness. Detailed simulations are discussed that quantify the level at which
false events from our search phase would start to to arise, and the
completeness of our search as a function of both SN brightness and host galaxy
redshift. The number of Type Ia and Type II SNe expected as a function of
redshift in the two HDF epochs are discussed in relation to several published
predictions and our own detailed calculations. A mean detection frequency of
one SN per epoch for the small HDF area is consistent with expectations from
current theory.Comment: 62 pages, 17 figures, ApJ 1999 in pres
Spectral Signatures of Gravitationally Confined Thermonuclear Supernova Explosions
We consider some of the spectral and polarimetric signatures of the
gravitational confined detonation scenario for Type Ia supernova explosions. In
this model, material produced by an off-center deflagration (which itself fails
to produce the explosion) forms a metal-rich atmosphere above the white dwarf
surface. Using hydrodynamical simulations, we show that this atmosphere is
compressed and accelerated during the subsequent interaction with the supernova
ejecta. This leads ultimately to the formation of a high-velocity pancake of
metal-rich material that is geometrically detached from the bulk of the ejecta.
When observed at the epochs near maximum light, this absorbing pancake produces
a highly blueshifted and polarized calcium IR triplet absorption feature
similar to that observed in several Type~Ia supernovae. We discuss the
orientation effects present in our model and contrast them to those expected in
other supernova explosion models. We propose that a large sample of
spectropolarimetric observations can be used to critically evaluate the
different theoretical scenarios.Comment: 4 pages, 3 figures. To appear in ApJ Letters. For higher resolution
images and movies see http://panisse.lbl.gov/~dnkasen/gcd.htm
Pre-Maximum Spectropolarimetry of the Type Ia SN 2004dt
We report observations of SN 2004dt obtained with the Very Large Telescope of
the European Southern Observatory on August 13.30, 2004 when the supernova was
more than a week before optical maximum. SN 2004dt showed strong lines of
\ion{O}{1}, \ion{Mg}{2}, \ion{Si}{2}, and \ion{Ca}{2} with typical velocities
of absorption minimum around 17,000 \kms. The line profiles show material
moving at velocities as high as 25,000 \kms in these lines. The observations
also reveal absorption lines from \ion{S}{2} and \ion{Si}{3} with a velocity of
only 11,000 \kms. The highest velocity in the \ion{S}{2} features can be traced
no higher than 15,000 \kms, much lower than those of O, Mg, Si, and Ca. SN
2004dt has a polarization spectrum unlike any previously observed. The
variation of the polarization across some \ion{Si}{2} lines approaches 2%,
making SN 2004dt the most highly polarized SN Ia ever observed. In contrast,
the strong line of O I at 777.4 nm shows little or no polarization signature.
The degree of polarization points to a richly-structured partially burned
silicon layer with substantial departure from spherical symmetry. A geometry
that would account for the observations is one in which the distribution of
oxygen is essentially spherically symmetric, but with bubbles of
intermediate-mass elements with significant opacity within the oxygen
substrate.Comment: Submitted to Ap
VLT Spectropolarimetry of the fast expanding Type Ia SN2006X
Using VLT-FORS1 we performed optical spectropolarimetric observations of the
Type Ia SN2006X on 7 pre-maximum epochs (day -10 to day -1) and one
post-maximum epoch (+39 days). The SN shows strong continuum interstellar
polarization reaching about 8% at 4000A, characterized by a wavelength
dependency that is substantially different from that of the Milky-Way dust
mixture. Several SN features, like SiII 6355A and the CaII IR triplet, present
a marked evolution. The CaII near-IR triplet shows a pronounced polarization
(~1.4%) already on day -10 in correspondence with a strong high-velocity
feature (HVF). The SiII polarization peaks on day -6 at about 1.1% and
decreases to 0.8% on day -1. By day +39 no polarization signal is detected for
the SiII line, while the CaII IR triplet shows a marked re-polarization at the
level of 1.2%. As in the case of another strongly polarized SN (2004dt), no
polarization was detected across the OI 7774A absorption. The fast-expanding
SN2006X lies on the upper edge of the relation between peak polarization and
decline rate, and it confirms previous speculations about a correlation between
degree of polarization, expansion velocity, and HVF strength. The polarization
of CaII detected in our last epoch, the most advanced ever obtained for a Type
Ia SN, coincides in velocity with the outer boundary of the Ca synthesized
during the explosion (15,000-17,000 km/s) in delayed-detonation models. This
suggests a large scale chemical inhomogeneity as produced by off-center
detonations, a rather small amount of mixing, or a combination of both effects.
In contrast, the absence of polarization at the inner edge of the Ca-rich layer
(8000-10,000 km/s) implies a substantial amount of mixing in these deeper
regions.Comment: 28 pages, 39 figures, accepted for publication in Astronomy and
Astrophysic
A spectropolarimetric view on the nature of the peculiar Type I SN 2005hk
We report two spectropolarimetric observations of SN 2005hk, which is a close
copy of the "very peculiar" SN 2002cx, showing low peak luminosity, slow
decline, high ionization near peak and an unusually low expansion velocity of
only about 7,000 km s^-1. Further to the data presented by Chornock et al.,
(2006), at -4 days before maximum, we present data of this object taken on 9
November 2005 (near maximum) and 23 November (+ two weeks) that show the
continuum and most of the spectral lines to be polarized at levels of about
0.2-0.3%. At both epochs the data corresponds to the Spectropolarimetric Type
D1. The general low level of line polarization suggests that the line forming
regions for most species observed in the spectrum have a similar shape to that
of the photosphere, which deviates from a spherical symmetry by <10%. In
comparison with spectropolarimetry of Type Ia and Core-collapse SNe at similar
epochs, we find that the properties of SN 2005hk are most similar to those of
Type Ia SNe. In particular, we find the low levels of continuum and line
polarization to indicate that the explosion mechanism is approximately
spherical, with homogeneous ejecta (unlike the chemically segregated ejecta of
CCSNe). We discuss the possibility that SN 2005hk was the result of the pure
deflagration of a white dwarf and note the issues concerning this
interpretation.Comment: ApJ accepted, uses emulateapj, 16 pages, 10 figures, figures 3 and 4
update
Spectropolarimetry of the Type Ia SN 2007sr Two Months After Maximum Light
We present late time spectropolarimetric observations of SN 2007sr, obtained
with the VLT telescope at ESO Paranal Observatory when the object was 63 days
after maximum light. The late time spectrum displays strong line polarization
in the CaII absorption features. SN 2007sr adds to the case of some normal Type
Ia SNe that show high line polarization or repolarization at late times, a fact
that might be connected with the presence of high velocity features at early
times
The Luminous and Carbon-Rich Supernova 2006gz: A Double Degenerate Merger?
Spectra and light curves of SN 2006gz show the strongest signature of
unburned carbon and one of the slowest fading light curves ever seen in a type
Ia event (Delta m_15 = 0.69 +/- 0.04). The early-time Si II velocity is low,
implying it was slowed by an envelope of unburned material. Our best estimate
of the luminosity implies M_V = -19.74 and the production of ~ 1.2 M_sun of
56Ni. This suggests a super-Chandrasekhar mass progenitor. A double degenerate
merger is consistent with these observations.Comment: Accepted for publication in ApJL (5 pages, 4 figures). UBVr'i' light
curves, UVOIR light curves, and spectra available at
http://www.cfa.harvard.edu/supernova/SN2006g
Connecting RS OPh to [some] Type Ia Supernovae
Aims: Recurrent nova systems like RS Oph have been proposed as a possible
channel to Type Ia Supernova explosions, based on the high mass of the
accreting white dwarf. Additional support to this hypothesis has been recently
provided by the detection of circumstellar material around SN2006X and
SN2007le, showing a structure compatible with that expected for recurrent nova
outbursts.In this paper we investigate the circumstellar environment of RS Oph
and its structure, with the aim of establishing a firmer and independent link
between this class of objects and Type Ia SN progenitors.
Methods: We study the time evolution of CaII, NaI and KI absorption features
in RS Oph, before, during, and after the last outburst, using multi-epoch,
high-resolution spectroscopy, and applying the same method adopted for SN2006X
and SN2007le.
Results: A number of components, blue-shifted with respect to the systemic
velocity of RS Oph, are detected. In particular, one feature strongly weakens
in the first two weeks after the outburst, simultaneously with the
disappearance of very narrow P-Cyg profiles overimposed on the much wider nova
emission lines of H, He, FeII and other elements.
Conclusions: We interpret these facts as the signature of density
enhancements in the circumstellar material, suggesting that the recurrent
eruptions might indeed create complex structures within the material lost by
the donor star. This establishes a strong link between RS Oph and the
progenitor system of the Type Ia SN2006X, for which similar features have been
detected.Comment: 8 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
- …